Cyanobacteria, which appeared on Earth some 200 million years before the The Great Oxygenation Event, initiated generating oxygen by photosynthesis. Before the GOE, any free oxygen they created was chemically seized by dissolved iron or organic matter. The GOE was the certain point when these oxygen basins turn out to be saturated and could not capture all of the oxygen that was formed by cyanobacterial photosynthesis. After the The Great Oxygenation Event, the additional free oxygen started to gather in the atmosphere.
Free oxygen is poisonous to obligate anaerobic creatures, and the growing concentrations may have wiped out maximum of the Earth’s anaerobic inhabitants at the time. Cyanobacteria were thus accountable for one of the most important extinction events in Earth’s history.